This M.Y. answer provides a list of permissible learning items on Tish'a B'Av. All these items are somehow related to the themes of mourning, the Temple destruction, etc.
Avot D'Rav Natan has several Mishnayot that seem to relate to the theme of Tish'a B'Av related to the setruction of Jerusalem. Examples:
Avot D'Rav Natan 4:4 and 4:5 Rav Yohanan ben Zakkai's request from Vespasian for Yavneh
Avot D'Rav Natan 6:3 Near the end of Mishnah; story of Kalba Savu'a who had enough food to feed everyone in Jerusalem for 22 years. Yet, the Zealots destroyed his storehouses
Would it be appropriate to learn these? Why weren't these included in the list?